A typical engine control system for a modern internal combustion engine includes an electronic controller operable to monitor engine operating conditions and operator inputs, and operable to control various systems and actuators based upon the monitored conditions and inputs. The typical engine control system is electrically connected to a plurality of engine and vehicle sensors which monitor engine operating conditions and operator demands. Monitored operating conditions may include, for example, engine rotational speed and position, engine load, vehicle speed, engine coolant temperature, intake air temperature, engine air/fuel ratio, accessory demands, and the operator's demand for power. The engine control system is operably connected to engine and powertrain actuators and systems that act to control the engine, in response to the engine operating conditions and operator demands. Typical actuators and systems include, for example, fuel injectors, fuel pump, idle air control valve, exhaust gas recirculation valve, throttle control valve, cam phasing actuator, valve actuators, transmission solenoids, and an exhaust system. A skilled practitioner designs and implements software algorithms and calibrations which are executed in the electronic controller to monitor the engine operating conditions and operator demands, and control the engine actuators accordingly. The software algorithms and calibrations are typically inserted into software of the engine controller during engine development, prior to start of production.
The control system includes a fuel system operable to precisely meter a quantity of fuel to the engine to meet operator demands for power and to meet increasingly stringent emissions requirements. The fuel system for the conventional spark-ignition, multi-cylinder engine typically includes a fuel tank with a fuel pump that is capable of pumping a volume of high pressure fuel through a fuel line to a fuel rail, for distribution to a plurality of fuel injectors. Typically a fuel injector corresponds to each cylinder of the engine. Each fuel injector is preferably positioned to deliver a quantity of fuel through a runner of an intake manifold of the engine so the fuel is delivered at or near an intake valve to the cylinder. A typical fuel injector comprises a solenoid valve that opens and closes a pintle valve in response to an electrical signal delivered by the engine controller. An injector calibration, in the form of a lookup table or an equation, is inserted into the software of the engine controller for use by the control algorithms. The injector calibration consists of a range of mass fuel flow values which correspond to a range of open times of the injector solenoid.
A primary function of the fuel control delivery system is to deliver a requisite mass of fuel to the engine to meet operator demands while also ensuring the engine meets the requisite emissions requirements. The engine controller operates to determine a mass amount of fuel to deliver to a cylinder, based upon engine operating conditions and operator demands. The controller further calculates an amount of time, or pulsewidth, the corresponding fuel injector must be open to deliver the mass amount of fuel to the cylinder, based upon the calibration. The controller actuates the injector solenoid for the calculated pulsewidth to deliver the appropriate mass amount of fuel. The engine controller typically uses correction factors to adjust the calculated pulsewidth to accommodate minor differences caused by variations between engines and engine components, and variations over the life of an engine.
The ability of the control system to accurately deliver a quantity of fuel is affected by the temperature at the point of delivery, i.e., at a tip of each fuel injector. An internal combustion engine is subjected to a range of ambient temperatures and operating temperatures, as is well-known. Temperature variations in and around the engine and its components may affect fuel density, thus affecting the mass of fuel delivered per unit of time. Temperature variations may have an effect on opening and closing characteristics of a fuel injector, thus affecting the mass of fuel delivered per injection event. Engineers have documented a shift in mass of fuel delivered by as much as 15% due to high ambient temperatures, and as much as 20% under hot restart conditions. This shift in delivery of mass of fuel is attributable to changes in fuel injector performance due to injector operating temperature. Operating temperature has been shown to affect injector opening and closing performance, thus affecting fuel flow during fuel injector opening and closing. Fuel density is affected by changes in fuel temperature as it passes through the fuel system and the fuel injector. Therefore, there is a need to develop an engine control system that accurately delivers a predetermined quantity of fuel, unaffected by the temperature at the point of delivery. The intended result is to improve fuel control and reduce fueling errors over a range of ambient temperatures and ambient conditions, especially during a hot-restart condition, thus improving driveability and emissions performance. The invention may also permit design improvements in fuel injectors and related components that take advantage of the performance enhancements gained with the invention.